Many switch mode power supply waveforms show large voltage spikes caused by interrupting current through the leakage inductance of the main transformer. These spikes occur across the primary power supply switch and the output rectifier when they turn off and also across the main transformer's primary and secondary windings. Controlling voltage stress is one of the main problems in power supply design. Voltage stress may be addressed by: (a) maximizing efficiency by allowing voltage stress and the electromagnetic interference (EMI) it generates; (b) dissipating voltage stress as heat in passive snubbers and clamps; (c) using an “active clamp” to limit voltage stress with transistors and lumped element circuits; or (d) using a “clamp winding” to limit voltage stress with a dedicated winding in the main transformer. These techniques either dissipate voltage stress as heat or return leakage inductance energy back into the power supply each power switching cycle.